One in a hundred children is born with a heart defect. Some children require heart surgery within the first few days of life, while others can wait until they are older. A complication of open-heart surgery is low blood flow due to the heart-lung machine that can cause sudden loss of kidney function known as acute kidney injury (AKI). AKI causes complications that can increase hospital length of stay and increase risk of death. Current ways to identify AKI are not able to it until 2 or 3 days after it has occurred. Because of this, there is not a specific treatment for AKI. If the investigators diagnose AKI early, they might be able to treat it and improve outcomes in children. NIRS is a skin monitor that can detect low blood flow to the kidney and might help diagnose AKI when it occurs in the operating room. The use of NIRS to diagnose AKI early is the focus of this study.

Near infrared spectroscopy (NIRS) is a noninvasive tool used for continuous monitoring of regional tissue oxyhemoglobin saturation. Sensors are placed on the head and abdomen or flank and use light to measure the percent oxygen levels in tissues. Head NIRS has been correlated with oxygen levels of the blood returning from the brain, and an abrupt decline in post-operative cardiac patients has been shown in retrospective studies to predict an impending event such as cardiac arrest. Animal studies have demonstrated that somatic NIRS monitoring is able to detect flow-induced changes in regional oxygen levels of the kidney and gut directly under the sensor. Unlike cerebral NIRS monitoring, there is no data regarding the clinical utility of NIRS over the abdomen and flank in predicting outcomes. Children are at risk of decreased organ perfusion following cardiac surgery, and is a phenomenon termed low cardiac output syndrome (LCOS). It occurs in approximately 25% of neonates and young children following cardiac surgery. The effects of LCOS on end organ function, specifically the kidney may result in acute kidney injury, thereby increasing morbidity and mortality. The incidence of acute kidney injury (AKI) following cardiac surgery is reported as high as 40%. The use of NIRS in the operating room to detect AKI in pediatric patients undergoing cardiac surgery is the focus of this proposal Specific Aim 1: Determine if a reduction in renal NIRS intra-operatively identifies patients with AKI Hypothesis: Reduced intra-operative renal NIRS will precede the diagnosis of acute kidney injury by an increase in serum creatinine within 1 to 3 days post-cardiopulmonary bypass Specific Aim 2: Determine if a reduction in renal NIRS intra-operatively correlates with increases in emerging biomarkers of AKI.

Hypothesis: Reduced intra-operative renal NIRS will precede the development if AKI as detected by neutrophil gelatinase-associated lipocalin, IL-6 and IL-18 by at least 2 hours.

Inclusion Criteria:

• All children less than or equal to age 4 undergoing cardiac surgery with the use of cardiopulmonary bypass at Colorado Children's Hospital

Exclusion Criteria:

• Prior enrollment in the study
• Agre greater than 4 years
• Use of nephrotoxic drugs within 48 hours of surgery
• Underlying renal dysfunction (preoperative estimated Schwartz clearance less than 80ml/min/1.73m2)
• Gestational age less than 34 weeks at the time of surgery
• Withdrawal of care planned

All children undergoing cardiac surgery with the use of cardiopulmonary bypass at our institution.